The present invention relates to a low pressure warning system for a pneumatic tire, and more particularly for a runflat tire.
Loss of tire pressure can result from a variety of causes such as a deteriorated seal between the tire and rim or a tire puncture by a sharp object. Various methods have been devised for enabling the safe continued operation of deflated or under-inflated (flat) tires without damaging the tire further and without compromising vehicle handling while driving to where the tire can be changed. Tires designed for continued operation under deflated or under-inflated conditions are referred to as xe2x80x9cextended mobility technologyxe2x80x9d tires or xe2x80x9cEMTxe2x80x9d tires. They are also called xe2x80x9crunflatxe2x80x9d tires, since they are capable of being driven when flat. The runflat tire""s structure alone has sufficient strength to support the vehicle load when the tire is deflated.
There are numerous support structures that can be incorporated into the tire or rim construction to impart runflat capability. For example, U.S. Pat. No. 4,111,249 discloses a runflat tire having an annular compression band (hoop) of solid high-strength metal or reinforced composite, located below the tread, either under or within the carcass. U.S. Pat. No. 4,059,138 discloses a runflat tire having, around the metal hub, an elastomeric ring that supports the inner central portion of the carcass when the tire is deflated.
The most common support structures to impart runflat capability are wedge inserts (xe2x80x9cinsertsxe2x80x9d), which are fillers generally having a crescent shaped cross-section, located within the sidewall, which is the region in the tire experiencing the greatest flex under load. The inserts reinforce (stiffen) the sidewall to avoid sidewall buckling during runflat operation (i.e. while running under-inflated).
For a conventional (non-runflat) tire, it is important for the driver to be immediately aware of a deflated condition, so that he can repair the tire as soon as possible to minimize running the tire when deflated, because operating a non-runflat tire when deflated can quickly degrade and/or damage the tire and rim.
Even with a runflat tire, which is meant to be driven deflated, a driver must be immediately aware of a deflated condition, so that he can minimize operating the tire when deflated. During runflat operation, due to the relatively large mass of material (including inserts) in the runflat tire""s sidewalls, heat builds up from cyclical flexure of the sidewalls. If driven in runflat operation for a prolonged period, the heat can degrade the inserts and other tire components and will eventually cause the inserts to fail, resulting in the very inconvenience and damage that the insert was intended to avoid. Additionally, the hysteresis of the material of the relatively thick sidewalls contributes to material fatigue and rolling resistance (which reduces fuel efficiency).
A conventional (non-runflat) tire""s sidewalls and tread continually buckle and flop as they rotate when driven while flat, so the driver can usually sense the existence of the flat through the resulting sounds he hears and the vibrations he feels. In contrast, a runflat tire""s sidewalls and tread do not collapse or buckle, unless they have been driven in runflat operation to the point of failure. Runflat inserts often operate so smoothly that the driver is unaware of a tire deflation and can continue to drive until the insert eventually fails.
Numerous tire deflation indicators (or alarms) have been disclosed in the patent literature, although few of them particularly for a runflat tire. Many tire deflation indicators include a pressure sensor and radio frequency transmitter within the tire cavity and a receiver outside the tire cavity. These designs have the disadvantage of high cost and difficulty of conveying electric power to the components in the tire cavity. Other tire deflation indicators entail sensing the difference in rotational speeds between the vehicle""s four tires. They are costly to implement and suffer from interferences. Other tire deflation indicators include an electronic pressure sensor attached to a valve stem or tube leading to the tire cavity. These have the difficulty of conveying electric power to the rotating components. Other tire deflation indicators include a mechanical pressure responsive mechanism attached to a valve stem or tube exiting the rim. These add complexity to the rim construction. Other tire deflation indicators have a xe2x80x9cfeelerxe2x80x9d rod, connected to a switch, that activates the switch when it contacts the bulging tire sidewall or the road surface. These mechanisms are cumbersome and prone to breakage.
To avoid some of the disadvantages of the aforementioned deflation indicators, several tire deflation indicators are disposed within the tire cavity and do not require electric power. For example, some tire deflation indicators have an insert (either in the sidewall or tire cavity) having nonuniform radius to cause wheel vibration in runflat operation to alert the driver. These designs can be costly and yield an uncomfortable runflat ride. U.S. Pat. No. 3,154,048 discloses a tire deflection warning device positioned within the tire""s interior, having a metal knocker and a spring, both positioned between a wheel rim and belt around the rim. When the tire flexes inwardly, the knocker is brought suddenly against the steel rim with each tire rotation to create a loud noise. U.S. Pat. No. 4,476,455 discloses an inflation warning device in which a ball strikes the wall of a case upon each revolution when the tire is deflated. U.S. Pat. Nos. 4,487,154 and 4,201,147 disclose low pressure warning devices having a striker or hammer that strikes the wheel rim when the pressure is low. Other low tire pressure alarms are disclosed in U.S. Pat. Nos. 3,030,911; 4,353,322; 4,580,519; and 5,207,173. These designs are prohibitively costly, can degrade wheel balance, and have rotating metal junctions that can corrode or seize. Some of them depend on centrifugal force to work, which renders them inoperative at slow speeds.
U.S. Pat. No. 1,195,883 discloses a xe2x80x9cleak-alarm for pneumatic tiresxe2x80x9d having a whistle fitted to a rubber bulb that is vulcanized to, or made an integral part of, an inner tube. When the inner tube is deflated, the bulb is xe2x80x9ccompressed, forcing the air from the bulb through the whistle and sounding the alarmxe2x80x9d. This has the disadvantages of requiring a specially-made inner tube and causing tire imbalance. Even if the device is applied to a tubeless tire (which is not disclosed), it would require a specially-made tire and cause tire imbalance.
U.S. Pat. No. 3,489,998; 3,659,264; 4,067,376 and 4,103,282 disclose various tire pressure warning systems entailing components mounted to vehicle wheel that, in response to low inflation, produce an acoustic (sonic or ultrasonic) vibration that is sensed by a receiver outside the tire, to generate a warning signal to the driver. These systems are not responsive to tread deflection.
It is desirable to have a alarm that is responsive to tread deflection so that it warns of heavy vehicle load along with low pressure. It is desirable to have a tread deflection alarm that is simple, low cost, light, not affecting tire balance, adaptable to standard tires and rims without alteration, out-of-sight (concealed within the tire), and not requiring electric power.
According to the present invention, a tire assembly comprises a tire (such as a runflat tire), a rim having a rim well; and an alarm system. The tire assembly is characterized by the alarm system having a belt disposed tightly around the rim well and a first bladder attached to the belt. The alarm system can include a first whistle attached to the first bladder disposed within the tire cavity.
The alarm system can have a second bladder with a second whistle attached to the belt on the opposite side of the rim well from the first bladder. Alternatively, the alarm system can have a counterweight attached to the belt on the opposite side of the rim well from the first bladder.
Both the first and second whistles emit an audible whistle when air passes through them in either the inhale and/or exhale directions. The whistles can also emit an ultrasonic whistle at a distinct frequency; and the tire assembly also has, disposed outside the tire cavity, an electronic circuit that is sensitive to the distinct ultrasonic frequency and can distinguish the whistle of the whistle from environmental noise. The circuit can distinguish the whistle sound from environmental noise based on frequency and periodicity.
In another embodiment, the first bladder is connected to a percussion noise-making mechanism within the tire cavity.